This paper 1 presents advances in techniques for representing OFDM signals in nonlinear RF power amplifier behavioural modelling. OFDM is significantly sensitive to nonlinear distortion because of the high peak to average power ratio (PAPR) of its envelope. Four signal representation techniques are presented and compared. These are Direct Time Domain method (DTD), Mixed Frequency and Time Domain method (MFTD), Statistical approach (Stat), and MFTD combined with a Modified Stat approach (MFTD-MS). All four are applied to a Bessel Fourier behavioural model for a GaN nonlinear PA. This model is a particularly suitable tool for large dynamic range nonlinearity analysis of certain classes of multicarrier signals. The goal is to compare accuracy, preservation of modulation information, complexity and computer resource consumption.
The IMP distortion occurring with the amplification of OFDM signals through a nonlinear RF power amplifier (PA) is analysed with a view to establishing internal relations and impairment significance of different types and combinationscomposition categories-of IMPS. Through this, a novel estimation method was deduced to calculate power spectral densities (PSD) of nonlinear distortion. This method also helps expose some PA independent and operating point (OP) independent characteristics of PSD of nonlinear distortion. The simulation and analysis is based on the use of an IEEE 802.11a OFDM signal and a nonlinear PA model is derived from envelope characteristic measurements of an X-band and S-band GaN power amplifier.
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